1. Field of the Invention
The present invention relates to a method for producing a solid-state imaging device configured by mounting an imaging element such as a CCD on a base.
2. Related Background Art
Solid-state imaging devices are used widely for video cameras and still cameras, and the like, and are provided in a form of a package in which an imaging element such as a CCD is mounted on a base made of an insulation material and a light-receptive region is covered with a transparent plate. In order to miniaturize the device, the imaging element is mounted on the base while keeping a bare chip state (or example, see JP 2002-43554 A). A conventional example of such solid-state imaging devices will be explained with reference to FIG. 9.
A base 31 in FIG. 9 has a frame form in planar shape with an aperture 32 in its central portion and a cross-sectional shape having uniform thickness as a whole. A bottom surface of the base 31 is provided with a wiring 33 made of a plated gold layer, which extends from the vicinity of the aperture 32 to an outer peripheral end face. On the surface of the base 31 on which the wiring 33 is provided, an imaging element 4 such as a CCD and the like is mounted, with the light-receptive region 4a of the imaging element 4 facing the aperture portion 32. On the top surface of the base 31, a transparent plate 5 made of glass is attached so as to cover the aperture 32. The periphery of the imaging element 4 is filled with a sealing resin 6 so as to hermetically seal a gap between the end portion of the imaging element 4 and the base 31. As mentioned above, the light-receptive region 4a is placed within a closed space formed in the aperture 32.
On the same plane as that of the light-receptive region 4a of the image element 4, an electrode pad (not shown) connected to a circuit of the light-receptive region 4a is placed, and a bump (protrusion electrode) 7 is provided on the electrode pad. An internal end portion of the wiring 33 adjacent to the aperture 32 forms an internal terminal portion 33a, which is connected to the electrode pad of the imaging element 4 via the bump 7.
This solid-state imaging device is mounted on a circuit board with the side of the transparent plate 5 facing upward as shown in the drawing. A portion of the wiring 33 placed on the bottom surface of the outer peripheral end portion of the base 31 forms an external terminal portion 33b, which is used for the connection with an electrode on the circuit board. The external terminal portion 33b of each wiring 33 is provided with a solder ball 8, which is used for the connection with an electrode on the circuit board. Furthermore, the solder ball 8 also has a function of maintaining the base 31 at an appropriate height from the surface of the circuit board.
The upper part of the transparent plate 5 is to be provided with lens barrel (not shown) having an imaging optical system in a manner in which a relative positional relationship with the light-receptive region 4a is set at a predetermined accuracy. Through the imaging optical system incorporated in the lens barrel, light from an object to be imaged is collected onto the light receiving region 4a and a photoelectric conversion is carried out.
However, it is difficult to obtain a sufficient flatness of the base 31 with the configuration of the above-mentioned conventional solid-state imaging device. That is to say, since the base 31 has a frame shape with the aperture portion 32, when resin molding is carried out, a curl and a warp in the cross-sectional shape may be generated. When the flatness of the surface on which the imaging element 4 is mounted is insufficient, the position of the imaging element 4 becomes unstable. As a result, the position of the lens barrel with respect to the light-receptive region 4a cannot be determined accurately.
Furthermore, although there is no description in JP2002-43554 A, in the conventional examples, since the wiring 33 is formed by plating, a process for applying the plating to the base 31 is complicated, which may lead to a high cost, and further the formed wiring 33 tends to have variation in dimensional accuracy.